Headers: fix _Unwind_{G,S}etGR for non-EHABI targets

The EHABI definition was being inlined into the users even when EHABI
was not in use.  Adjust the condition to ensure that the right version
is defined.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@309327 91177308-0d34-0410-b5e6-96231b3b80d8